Graphene dispersion

ABSTRACT

A graphene dispersion is provided. The graphene dispersion is formed by a graphene powder and a processing solvent, wherein the graphene in the graphene dispersion has an average diameter of 0.5 μm to 1 μm, 3 to 5 layers, a solid content of 5% to 50%, and a residue oxygen content less than 1 wt %, and after being left to stand for 12 hours, the graphene dispersion has a distribution concentration increasing from the top section to the bottom section of the storage container, a viscosity of 5000 cps to 8000 cps, and a graphene concentration of 20 wt %.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of and claims the prioritybenefit of U.S. application Ser. No. 15/705,274, filed on Sep. 15, 2017,now allowed. The prior U.S. application Ser. No. 15/705,274 claims thepriority benefit of Taiwan application serial no. 105137512, filed onNov. 16, 2016. The entirety of each of the above-mentioned patentapplications is hereby incorporated by reference herein and made a partof this specification.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to an air flow generating device, a graphenedispersion, and a preparation method thereof, and more particularly, toan air flow generating device for preparing a graphene powder with lowoxygen content, a graphene dispersion, and a preparation method thereof.

Description of Related Art

Graphene has a two-dimensional structure formed by carbon atoms bondedwith sp² covalent bonds, and has special properties such as a relativelyhigh carrier mobility, hardness, thermal conductivity, and large surfacearea. Therefore, in recent years, graphene has become a highly-valuedresearch target in fields such as medicine, electronics, andoptoelectronic components. At the same time, the graphene dispersion,which is composed of graphene and a specific solvent, can be extensivelyapplied in the coating field, and is an important additive in productssuch as conductive coatings and auxiliaries thereof, lithium ionelectrode auxiliaries, anti-corrosion coating additives, and grapheneheat spread films.

However, the known graphene dispersion preparation technique hasdisadvantages for commercialization such as waste water pollution andtoxic waste exhaust issues in chemical modification process, cost issuesrelated to lower carbon yield for physical method, for example,mechanical peeling, ultrasonic oscillation, and ball milling method.These above disadvantages will strongly increase the cost and difficultyof production management. Moreover, current commercial products ofgraphene dispersion mostly have low solid content (usually lower than1%), wherein excess solvent significantly causes subsequent resinproperties and the following processability problems for lesscontrolling rheology or viscosity, and therefore these commercialproducts are not suitable for application in the coating field.Moreover, although surface modification and excess dispersing agent(greater than 5%) could enhance the dispersion of graphene, both maydestroy intrinsic properties of graphene coating by structure damage andinterconnection of blockage of graphene, which are respectivelygenerated along with chemical treatment and caused by coverage ofdispersion agent.

Based on the above, development of a graphene dispersion that can meetboth of environmental protection and commercialization needs with highsolid content, high production yield, variation option of solvent,controllable rheology of suspension, long stable duration of suspension,reliable quality of products, and low manufacturing cost is still acrucial problem for graphene industry.

SUMMARY OF THE INVENTION

The invention provides an air flow generating device for preparing agraphene powder with low oxygen content, a graphene dispersion, and apreparation method thereof. The graphene powder fabricated by the airflow generating device is used to prepare the graphene dispersion forsurmounting most of obstacles of current technical barriers in thepresent graphene dispersion process effectively. As a result, ahigh-concentration graphene dispersion having a specific concentrationvariation can be prepared to not only meet environmental needs, but alsohave significantly high solid content, good production yield, excellentsuspension, and homogenize product specifications, and to significantlyreduce the manufacturing cost of the graphene dispersion.

The graphene dispersion of the invention is formed by a graphene powderand a processing solvent using the preparation method of the graphenedispersion, wherein the graphene in the graphene dispersion has anaverage diameter of 0.5 μm to 1 μm, 3 to 5 layers, a solid content of 5%to 50%, and a residue oxygen content less than 1 wt %. The graphenedispersion of the invention has the nature of constant viscosity of 5000cps to 8000 cps, a graphene concentration of 20 wt %, and after beingleft to stand for 12 hours, a concentration distribution of the graphenedispersion increases from the top section to the bottom section in astorage container.

In an embodiment of the invention, the concentration difference betweenthe top section and the bottom section in the graphene dispersion is 0.1wt % to 20 wt %.

In an embodiment of the invention, the graphene powder has 5 to 10layers.

In an embodiment of the invention, the graphene powder has an averagediameter of 3 μm to 15 μm.

In an embodiment of the invention, the graphene powder has a residueoxygen content less than 0.1 wt %.

In an embodiment of the invention, the processing solvent includes ahydrocarbon solvent, a halogenated hydrocarbon solvent, an alcoholsolvent, a phenol solvent, a ketone solvent, an ester solvent, an ethersolvent, an acetal solvent, an acid solvent, an acid anhydride solvent,a nitrogen-containing compound solvent, a sulfur-containing compoundsolvent, a polyfunctional group solvent, or an inorganic solvent.

In an embodiment of the invention, the processing solvent has aninterfacial tension of 15 mN/m to 50 mN/m and a Hansen solubilityparameter of 5.0 MPa^(0.5) to 15 MPa^(0.5).

In an embodiment of the invention, based on the total weight of thegraphene dispersion, the amount of the graphene powder is 0.001 wt % to30 wt %.

In an embodiment of the invention, the processing solvent has a polarforce parameter of 0.5 MPa^(0.5) to 5.5 MPa^(0.5), a dispersing powerparameter of 7.0 MPa^(0.5) to 9.0 MPa^(0.5), and a hydrogen bond forceparameter of 2.0 MPa^(0.5) to 7.0 MPa^(0.5).

Based on the above, the air flow generating device of the inventionleads to a transformation from graphite raw materials to a graphenepowder with low oxygen content using a direct continuous physicalmethod, and the graphene powder has specific features of a narrowdistribution of layer number for the uniformity, a uniformed diameterdistribution for the following dispersion process with a low energy, andwell-crystalized structure for the good compatibility with the specificsolvent. At the same time, the invention provides a high solid contentgraphene dispersion utilized the graphene powder. The graphenedispersion has advantages such as high yield for the uniformity ofproducts and also for the benefit of cost, high and adjustable solidcontent for easy handling in the following process, and therefore theissues of low solid content and small solvent selection of graphenedispersion commercial products can be solved, such that processabilityand the adaptability to different coating processes can be improved tofacilitate application in the coating field.

In order to make the aforementioned features and advantages of thedisclosure more comprehensible, embodiments accompanied with figures aredescribed in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is the cross section of an air flow generating device.

FIG. 2 is a perspective view of the rotating awl of FIG. 1.

FIG. 3A is a schematic diagram of the top surface and bottom surface ofthe top of a rotating awl.

FIG. 3B is a schematic diagram of the top surface and bottom surface ofthe center of the rotating awl.

FIG. 3C is a schematic diagram of the top surface and bottom surface ofthe bottom of the rotating awl.

FIG. 4 is a flow schematic diagram of the manufacturing method of agraphene powder.

DESCRIPTION OF THE EMBODIMENTS

The invention provides an air flow generating device for preparing agraphene powder, a graphene dispersion, and a preparation methodthereof, wherein the graphene powder prepared by the air flow generatingdevice is used to prepare the graphene dispersion. In the following, thedetails of the air flow generating device, the graphene dispersion, andthe preparation method thereof of the invention are described.

<Air Flow Generating Device>

FIG. 1 is the cross section of an air flow generating device, and FIG. 2is a perspective view of the rotating awl of FIG. 1. Referring to bothFIG. 1 and FIG. 2, an air flow generating device 100 includes an outerbushing 110 and a rotating awl 120, wherein the outer bushing 110 has achamber 112, an intake opening 114, and an outtake opening 116. Theintake opening 114 is connected to the chamber 112 from below and theouttake opening 116 is connected to the chamber 112 from above, and thechamber 112 has a necked portion 112 a. The rotating awl 120 and thechamber 112 are conformally disposed in the chamber 112, and therotating awl 120 and the inner wall of the chamber 112 have a slitspacing 108 in between, wherein the rotating awl 120 includes a rotatingbody 122 and a plurality of screw threads 124, and the screw threads 124are distributed on the outer surface of the rotating body 122 from abottom 1221 of the rotating body 122 toward the top of the rotating body122 in a spiral manner.

In an embodiment, the quantity of the screw threads 124 can be between 8and 32, and the quantity of the screw threads 124 in another embodimentcan be between 12 and 18. The quantity of the screw threads 124 is notlimited by the description herein, and the designer can change thequantity of the screw threads 124 out of consideration of other factorsbased on actual need. Moreover, a top surface 120 a of the rotating awl120 and a top surface 112 b of the necked portion 112 a are level.

FIG. 3A is a schematic diagram of the top surface and bottom surface ofthe top of a rotating awl, FIG. 3B is a schematic diagram of the topsurface and bottom surface of the center of the rotating awl, and FIG.3C is a schematic diagram of the top surface and bottom surface of thebottom of the rotating awl. Referring to all of FIG. 3A, FIG. 3B, andFIG. 3C, the rotating body 122 can be divided into a bottom 1221, a top1222, and a center 1223 located between the bottom 1221 and the top1222, and since the screw threads 124 are formed on the outer surface(not shown) of the rotating body 122, cross sections of the rotating awl120 are taken along the circumferential direction of the rotating awl120, and the cross sections of the rotating awl 120 are substantiallystellate. The depth and width of the screw threads 124 can be designedbased on actual need.

Based on the above, the diameter of the rotating body 122 is decreasedfrom the bottom 1221 to the top 1222. More specifically, the diameter ofa bottom surface 1221 a of the bottom 1221 of the rotating awl 120 isgreater than the diameter of a top surface 1221 b of the bottom 1221,the diameter of a bottom surface 1223 a of the center 1223 is equal tothe diameter of the top surface 1221 b of the bottom 1221, and thediameter of the bottom surface 1223 a of the center 1223 is greater thanthe diameter of a top surface 1223 b of the center 1223, as shown inFIG. 3B and FIG. 3C. Moreover, the diameter of a bottom surface 1222 aof the top 1222 is equal to the diameter of the top surface 1223 b ofthe center 1223, and the diameter of the bottom surface 1222 a of thetop 1222 is greater than the diameter of a top surface 1222 b of the top1222, as shown in FIG. 3A and FIG. 3B. Due to the difference among thediameters of the bottom 1221, the center 1223, and the top 1222, thequantity of the screw threads 124 located in each portion is alsodifferent.

It should be mentioned that, the rotating body 122 can be integrallyformed or formed by the assembly of three columns having differentdiameters. The screw threads 124 located at the top 1222 of the rotatingbody 122 can be disposed at the same intervals, and an angle θ1 relativeto the top surface 1222 b or the bottom surface 1222 a of the top 1222is fixed, and is, for instance, 15 degrees to 35 degrees; the screwthreads 124 located at the center 1223 can also be disposed at the sameintervals, and an angle θ2 relative to the top surface 1223 b or thebottom surface 1223 a of the center 1223 is fixed, and is, for instance,35 degrees to 70 degrees; and the screw threads 124 located at thebottom 1221 can also be disposed at the same intervals, and an angle θ3relative to the top surface 1221 b or the bottom surface 1221 a of thebottom 1221 is fixed, and is, for instance, 70 degrees to 90 degrees.However, the angles of the screw threads 124 at the top 1222, the center1223, and the bottom 1221 are not exactly the same. For instance, theangle of the screw threads 124 located at the top 1222 is 25 degrees,the angle of the screw threads 124 located at the bottom 1221 is 60degrees, and the angle of the screw threads 124 located at the center1223 is about 42.5 degrees. Moreover, the angle of the screw threads 124at the junctions of the top 1222, the center 1223, and the bottom 1221can be adjusted in response to changes in diameter, and the angle can be35 degrees to 85 degrees.

When the air flow generating device 100 of FIG. 1 is used, the rotatingawl 120 rotates at a rotating speed of 3000 rpm to 7000 rpm in thechamber 112. In general, when the rotating awl 120 rotates in thechamber 112, if the outer surface of the rotating awl 120 and thesurface of the inner wall of the chamber 112 are smooth, then gasentering from the intake opening 114 is driven by the rotation of therotating awl 120 to produce a rotating air flow and is dissipated fromthe outtake opening 116 located at the top 1222 of the outer bushing110. Via the centrifugal force produced by the rotation of the rotatingawl 120, the rotating air flow produces some horizontal component, butcompared to the force of the air flow escaping upward from the outtakeopening 116, the horizontal component is not significant, and is almostnegligible.

In particular, via the screw threads 124 formed on the outer surface ofthe rotating body 122 in a spiral distribution, when gas enters thechamber 112 from the intake opening 114 and is driven by the rotatingawl 120 to form a rotating air flow, the centrifugal force guided by thescrew threads 124 makes the horizontal component of the rotating airflow significant.

Moreover, although the rotating awl 120 and the outer bushing 110 areconformal, the slit spacing 108 between the rotating body 122 and theinner wall of the chamber 112 changes from the bottom surface 1221 a ofthe bottom 1221 of the rotating body 122 to the top surface 1222 b ofthe top 1222 of the rotating body 122, and is, for instance, decreased.Such design method is based on a gas flux equation to compress the gasentering the air flow generating device 100 when flowing upward suchthat air flow is accelerated from bottom to top. Since the chamber 112provides one wide space S on the top surface of the top 1222 of therotating body 122, the air flow entering the wide space S after leavingthe rotating awl 120 is expanded, and is then dissipated from theouttake opening 116.

In short, the air flow introduced from the intake opening 114experiences the flow rate changes of slow, fast, and slow from thebottom 1221 to the top 1222 of the rotating awl 120, wherein since theair flow is immediately released to a relatively larger space S afterleaving the slit spacing 108 between the rotating awl 120 and the innerwall of the chamber 112, the volume of the gas is continuously andrapidly expanded.

The air flow generating device 100 allows the air flow to produce ahorizontal component via the screw threads 124 and the slit spacing 108,and after the air flow leaves the screw threads 124, the air flowproduces a continuous and rapid gas volume change in the unit space S,and therefore the production of graphene powder requiring anintercalation process can be facilitated.

<Graphene Powder>

Via the air flow generating device, a graphene powder with low oxygencontent can be manufactured. FIG. 4 is a flow schematic diagram of themanufacturing method of a graphene powder. In the following, themanufacturing method of a graphene powder floc of an embodiment of theinvention is described with FIG. 4.

First, referring to FIG. 4, step S110 is performed to perform acontinuous high-speed reciprocating rolling process on a graphite rawmaterial to form a graphite precursor, wherein the graphite precursorhas a dislocation slippage structure. In the present embodiment, theintercalation spacing in the graphite raw material is, for instance,3.354 Å. The graphite precursor has an intercalation spacing of, forinstance, 3.44 Å to 3.60 Å; an average particle size of, for instance,10 μm to 100 μm, preferably, for instance, 15 μm to 35 μm; an averagethickness of, for instance, 0.05 μm to 1 μm, preferably, for instance,0.3 μm to 0.8 μm; and a residue oxygen content of, for instance, lessthan 5%, preferably, for instance, less than 1%. Since the graphiteprecursor has a dislocation slippage structure, an intercalationreaction can be facilitated in a subsequent process. More specifically,a graphite precursor plate having a dislocation slippage structure canbe formed via the tangential stress on the plane of a continuoushigh-speed reciprocating rolling process, and then a graphite precursorpowder is formed via a dry high-speed polishing process.

Next, referring further to FIG. 4, step S120 is performed to subject thegraphite precursor to an intercalation reaction via horizontalcompressed air flow to form a graphene-gas intercalation compound. Inthe present embodiment, the wind velocity of the horizontal compressedair flow is, for instance Mach 0.3 to Mach 1, preferably, for instance,Mach 0.5 to Mach 0.8; and the air volume is, for instance, 186 CMM to619 CMM, preferably, for instance, 310 CMM to 495 CMM. Morespecifically, the horizontal compressed air flow can be a subcriticalfluid, and since the wind velocity is, for instance, Mach 0.3 or above,the horizontal compressed air flow can also be referred to as subsoniccompressible flow.

Next, referring further to FIG. 4, step S130 is performed to subject thegraphene-gas intercalation compound to a swelling/exfoliation processvia intercalation air pressure release to form a graphene aggregate.Next, as shown in FIG. 4, step S140 is performed to make the grapheneaggregate suspend, drift, and collide with one another in the air flow,such that a graphene powder is produced.

In the present embodiment, the graphene powder has the advantages offixed number of layers and consistent diameter feature. Morespecifically, the graphene powder has, for instance, 5 to 10 layers; thethickness is, for instance, 2.5 nm to 4.5 nm; the residue oxygen contentis, for instance, less than 0.1 wt %; and the bulk density is, forinstance, 0.001 g/cm³ to 2.24 g/cm³, preferably, for instance, 0.01g/cm³ to 0.5 g/cm³. The average diameter of the graphene powder is, forinstance, 3 μm to 15 μm, and more specifically, the average diameter is,for instance, 3 μm to 5 μm, 5 μm to 10 μm, or 10 μm to 15 μm, morepreferably, for instance, 3 μm to 5 μm.

<Graphene Dispersion>

The graphene dispersion of the invention is prepared with the graphenepowder and a processing solvent, wherein based on the total weight ofthe graphene dispersion, the amount of the graphene powder is, forinstance, 0.001 wt % to 30 wt %. Since the preparation of the graphenedispersion is performed using oligomeric graphene powder with low oxygencontent having a specific number of layers and a specific form, thegraphene powder has the feature of easy homogenization at low energywithout structural damage caused by oxidation based on thecharacteristics of fixed number of layers and uniform diameter. As aresult, the resulting graphene dispersion has advantages such as highyield, high solid content, and adjustable solid content.

More specifically, the preparation method of the graphene dispersion ofthe invention includes the following steps. First, a homogenizationprocess is performed on the graphene powder and the processing solventto prepare a graphene paste. Next, a layer-thinning process is performedon the graphene paste to prepare a homogeneous graphene dispersion. Inthe following, the details of the preparation method of the graphenedispersion of the invention are described.

Processing Solvent

In the present embodiment, the processing solvent can include ahydrocarbon solvent, a halogenated hydrocarbon solvent, an alcoholsolvent, a phenol solvent, a ketone solvent, an ester solvent, an ethersolvent, an acetal solvent, an acid solvent, an acid anhydride solvent,a nitrogen-containing compound solvent, a sulfur-containing compoundsolvent, a polyfunctional group solvent, or an inorganic solvent. Morespecifically, the processing solvent is, for instance, toluene, xylene(xyl), ethanol, isopropanol (IPA), butanol, acetone, ethyl acetate,butyl acetate (BAC), N,N-dimethylformamide (DMF), N-methylpyrrolidone(NMP), N,N-dimethylacetamide (DMAc), or water.

However, a suitable processing solvent for the invention is not limitedto the examples provided in the above, and other solvents having thefollowing properties can also be used as the processing solvent: aninterfacial tension of, for instance, 15 mN/m to 50 mN/m, preferably,for instance, 20 mN/m to 40 mN/m; a Hansen solubility parameter of, forinstance, 5.0 MPa^(0.5) to 15 MPa^(0.5); a polar force parameter of, forinstance, 0.5 MPa^(0.5) to 5.5 MPa^(0.5); a dispersing power parameterof, for instance, 7.0 MPa^(0.5) to 9.0 MPa^(0.5); and a hydrogen bondforce parameter of, for instance, 2.0 MPa^(0.5) to 7.0 MPa^(0.5). Morespecifically, based on the total weight of the graphene dispersion, theamount of the processing solvent is, for instance, 70 wt % to 99.99 wt%.

Homogenization Process

In the preparation method of the graphene dispersion of the invention, ahomogenization process is performed to form a graphene paste used as abyproduct for an intermediate process. In the homogenization process,the average diameter of the graphene powder is adjusted and changed byproducing normal direction stress to the graphene structure withoutchanging the graphene thickness to achieve the object of homogenizeddiameter. As a result, the suspension of graphene in the liquid can beeffectively extended, wherein the maximum dispersion duration canachieve 150 days or more, and also dispersant content can be limited.

In the present embodiment, two major processes of pre-mixing and severedispersion in homogenization are utilized, and homogenization viaequipment such as a DC mechanical mixer, planetary mixer, mixer, ballmill mixer, three roller mixer, single screw mixer, or double screwmixer, and therefore compared to a known process in which graphite isused as the raw material and graphene dispersion is obtained viadispersion, oxidation, peeling, and centrifugal processes, the inventioncan solve the issues of, for instance, low graphene content and reducedconductivity due to structural damage from oxidation present in priorart.

Graphene Paste

In the present embodiment, the features of the graphene paste contain:the graphene has an average diameter of, for instance, 0.1 μm to 1.5 μm,preferably, for instance, 0.3 μm to 0.8 μm; and the graphene has athickness of, for instance, 2.5 nm to 4.5 nm, a residue oxygen contentof, for instance, less than 0.5%, and a solid content of, for instance,5% to 50%, most preferably, for instance, 15% to 30%.

Layer-Thinning Process

In the preparation method of the graphene dispersion of the invention, alayer-thinning process is performed on the graphene paste to form ahomogeneous graphene dispersion. In the layer-thinning process, theaverage thickness of the graphene powder is changed by producing planedirection stress to the graphene structure without changing the graphenediameter to achieve the object of homogenized suspension. As a result,suspension time and allowable ratio of solid content can be increased.

In the present embodiment, the thin film process can contain twodifferent processes, which are respectively a mixing process and ahigh-energy dispersing process. More specifically, the mixing processcan be performed via, for instance, a five-axis mixing method, ball millmixing method, or shear mixing method, and in the high-energy shearprocess, heavy dispersion can be performed via, for instance, high-speedhomogenization or high-pressure crushing to form a homogeneous graphenedispersion.

Via the preparation method of the graphene dispersion of the invention,a high-concentration graphene dispersion having a specific concentrationvariation can be formed without the addition of any dispersant, andtherefore the graphene structure in the graphene dispersion is notaffected by excess dispersing aid, and good material properties areretained. More specifically, in the graphene dispersion of theinvention, the purity of the graphene is about 100%, and the averagediameter of the graphene in the graphene dispersion is, for instance,0.5 μm to 1 μm; the number of layers is, for instance, 3 to 5; the solidcontent is, for instance, 5% to 50%; the residue oxygen content ofgraphene is, for instance, less than 1 wt %; and the thickness is, forinstance, 0.8 nm to 4.5 nm, preferably, for instance, 1.0 nm to 2.0 nm.

Moreover, the concentration distribution of the graphene dispersion canbe increasing from the top section to the bottom section of the storagecontainer after being left to stand for 12 hours, the viscosity is, forinstance, 5000 cps to 8000 cps, and the graphene concentration is, forinstance, 20 wt %, wherein the concentration difference (C %) betweenthe top section and the bottom section of the storage container is, forinstance, 0.1 wt % to 20 wt %, preferably, for instance, 5 wt % to 15 wt%, and the maximum stable dispersion duration can achieve 150 days ormore.

In the following, the graphene dispersion provided by the invention isdescribed in detail via an experimental example. However, the followingexperimental example is not intended to limit the invention.

Experimental Example

To prove that the graphene dispersion of the invention is with highersolid content and stable dispersion, this experimental example isprovided below.

It should be mentioned that, since the preparation method of thegraphene dispersion is described in detail above, in the following,details relating to the preparation of the graphene dispersion areomitted for ease of explaining.

Preparation of Graphene Dispersion

Based on the preparation method of the graphene dispersion of theinvention, Table 1 provides each of the composition conditions andprocess conditions for the preparation of the graphene dispersions ofexample 1 to example 21. In Table 1, the mixing ratio (G/S) representsthe ratio of graphene/solvent.

TABLE 1 Graphene powder Homogenization process Layer-thinning processAverage Mixing Solid Processing Polishing Mixing Solid Processingdiameter Number of ratio content time bead density Processing ratiocontent time Dispersing (μm) layers (G/S) (phr) (hr) (g/cm³) solvent(G/S) (phr) (hr) solvent Example 1 10 to 15  8 to 10 1/10 10 48 5.7 NMP1/10 10 2 NMP Example 2  5 to 10  8 to 10 1/10 10 48 5.7 NMP 1/10 10 2NMP Example 3 3 to 5 6 to 8 1/10 10 48 5.7 NMP 1/10 10 2 NMP Example 4 3to 5 6 to 8 1/10 10 144 5.7 NMP 1/10 10 2 NMP Example 5 3 to 5 6 to 81/10 10 80 5.7 NMP 1/10 10 2 NMP Example 6 3 to 5 6 to 8 1/10 10 96 5.7NMP 1/10 10 2 NMP Example 7 3 to 5 6 to 8 1/10 10 144 5.7 NMP 1/10 10 2NMP Example 8 3 to 5 6 to 8 1/10 10 144 5.7 NMP 1/10 10 4 NMP Example 93 to 5 6 to 8 1/10 10 144 5.7 NMP 1/10 10 6 NMP Example 10 3 to 5 6 to 81/10 10 144 5.7 NMP 1/10 10 10 NMP Example 11 3 to 5 6 to 8 1/10 10 1445.7 NMP 2/10 20 10 NMP Example 12 3 to 5 6 to 8 1/10 10 144 5.7 NMP 3/1030 10 NMP Example 13 3 to 5 6 to 8 1/10 10 24 7.9 NMP 1/10 10 10 NMPExample 14 3 to 5 6 to 8 2/10 20 24 7.9 NMP 2/10 20 10 NMP Example 15 3to 5 6 to 8 3/10 30 24 7.9 NMP 3/10 30 10 NMP Example 16 3 to 5 6 to 81/10 10 24 7.9 IPA 1/10 10 10 IPA Example 17 3 to 5 6 to 8 2/10 20 247.9 IPA 2/10 20 10 IPA Example 18 3 to 5 6 to 8 1/10 10 24 7.9 BAC 1/1010 10 BAC Example 19 3 to 5 6 to 8 2/10 20 24 7.9 BAC 2/10 20 10 BACExample 20 3 to 5 6 to 8 1/10 10 24 7.9 Xyl 1/10 10 10 Xyl Example 21 3to 5 6 to 8 2/10 20 24 7.9 Xyl 2/10 20 10 Xyl

Evaluation 1: Property Evaluation of Graphene Dispersion

The graphene dispersions formed in example 1 to example 21 were measuredfor graphene average diameter, number of layers, and concentrationdifference (C %) between the top section and the bottom section of thestorage container after being left to stand for 12 hours, and theevaluation results are provided in Table 2 below.

The measurement method of the concentration difference of the dispersionincludes performing solid content analysis on the dispersion at ⅓ liquidheight and ⅔ liquid height of the storage container every 24 hours, andsubtracting the concentration C_(1/3)% at the ⅓ location from theconcentration C_(2/3)% at the ⅔ location to obtain the C % concentrationdifference, wherein the solid content is the concentration obtainedafter drying the liquid. If the concentration difference is greater than20% (i.e., (C_(1/3)%-C_(2/3)%)>20%), then dispersion is poor.

TABLE 2 Average Number of Concentration diameter (μm) layers difference(C %) Example 1  7 to 10  8 to 10 >50% Example 2 3 to 5  8 to 10 >50%Example 3 1 to 3 6 to 8 >30% Example 4 0.6 to 0.8 6 to 8 <15% Example 51.0 to 1.2 6 to 8 >20% Example 6 0.8 to 1.0 6 to 8 >20% Example 7 0.6 to0.8 4 to 6 <15% Example 8 0.6 to 0.8 3 to 5 <15% Example 9 0.6 to 0.8 3to 5 <15% Example 10 0.6 to 0.8 3 to 5 <15% Example 11 0.6 to 0.8 3 to 5<15% Example 12 0.8 to 1.0 3 to 5 >20% Example 13 0.6 to 0.8 3 to 5  <5%Example 14 0.6 to 0.8 3 to 5 <10% Example 15 0.6 to 0.8 4 to 6 <15%Example 16 0.6 to 0.8 3 to 5 8.89%  Example 17 0.6 to 0.8 3 to 5  <5%Example 18 0.6 to 0.8 3 to 5 18.91%  Example 19 0.6 to 0.8 3 to 5 <10%Example 20 0.6 to 0.8 3 to 5 3.42%  Example 21 0.6 to 0.8 3 to 5 <10%

It can be known from Table 2 that, the average diameter distribution ofthe graphenes of example 1 to example 21 formed using the preparationmethod of the invention is homogeneous, and therefore the issue ofuneven product diameter distribution in a known physical method such asmechanical exfoliation, ultrasonic oscillation, or ball milling can bealleviated. Moreover, after being left to stand for 12 hours, theconcentration distribution of the graphene dispersions of example 1 toexample 21 increases from the top section to the bottom section of thestorage container.

Evaluation 2: Property Comparison of Graphene Dispersion of Inventionand Commercial Product

The graphene dispersions formed in example 1 to example 21 and thecommercial products of comparative example 1 to comparative example 6were measured for the solid content of graphene and maximum suspensionduration, and the evaluation results are provided in Table 3 below.

The solid content is the concentration obtained after the liquid isdried. The definition of 150 days of suspension duration is definedbelow: measurement is taken on the 150th day after the dispersion isformed, and if the concentration difference is <20%, then the suspensionduration is at least 150 days. The measurement method of theconcentration difference is described above and is therefore notrepeated herein.

The commercial products of comparative example 1 to comparative example6 were formed by a known oxidation process and stripping process withoutthe homogenization process and layer-thinning process provided by theinvention, wherein the raw material of comparative example 1 tocomparative example 3 is graphite, and the raw material of comparativeexample 4 to comparative example 6 is graphene.

TABLE 3 Solid content Maximum suspension (phr) duration (days) Example 110 1 Example 2 10 1 Example 3 10 1 Example 4 10 150 Example 5 10 3Example 6 10 3 Example 7 10 150 Example 8 10 150 Example 9 10 150Example 10 10 150 Example 11 20 150 Example 12 30 3 Example 13 10 150Example 14 20 150 Example 15 30 30 Example 16 10 150 Example 17 20 150Example 18 10 30 Example 19 20 150 Example 20 10 150 Example 21 20 150Comparative 0.1 to 1 NA example 1 Comparative    0.05 NA example 2Comparative  0.02 to 0.2 example 3 Comparative 0.2 to 5 >90 example 4Comparative 0.0001 to 1   >7 example 5 Comparative 0.001 to 0.5  example6

It can be known from Table 3 that, compared to comparative example 1 tocomparative example 6 using a known oxidation process and exfoliationprocess, example 1 to example 21 using the preparation method of theinvention have significantly higher graphene solid content, andtherefore the preparation method of the invention can solve the issue oflow graphene solid content of commercial products to improveprocessability. As a result, application of the preparation method ofthe invention in the coating field can be facilitated. Moreover, asshown in Table 3, compared to the commercial products of comparativeexample 1 to comparative example 6, the preparation method of thegraphene dispersion of the invention can effectively increase thesuspension of graphene in a liquid, such that the stable dispersionduration can achieve 150 days.

Based on the above, in the invention, a low-oxygen contained graphenepowder with a specific number of layers is mainly formed by an air flowgenerating device, and a graphene dispersion utilizing a graphene powderwith a specific number of layers and high solid content, and thereforemajor issues for current commercial graphene dispersion products such aslow solid content and limited solvent options can be solved effectively,such that processability and adaptability in different coating processescan be improved to facilitate application in the coating field.Moreover, the graphene dispersion preparation method of the inventiondoes not require oxidation, surface modification, or addition of a largeamount of dispersing agent (>5%), and therefore the well crystallinityof graphene structure can be remained without structural damage duringthe oxidation process and also interfacial constrain resulted by theexcess dispersing agent, and leads to a good properties thereof.Moreover, issues of polluted water and toxic waste generated from theoxidation process in prior art can be further solved to achieve theenvironmental needs. As a result, the invention can effectively improvethe most of the current technical issues for the current graphenedispersion process such as increasing the yield and purity, providing auniform distribution, and enhancing the stabilization duration of thegraphene dispersion.

Although the invention has been described with reference to the aboveembodiments, it will be apparent to one of ordinary skill in the artthat modifications to the described embodiments may be made withoutdeparting from the spirit of the invention. Accordingly, the scope ofthe invention is defined by the attached claims not by the abovedetailed descriptions.

What is claimed is:
 1. A graphene dispersion formed by a graphene powderand a processing solvent, wherein a graphene in the graphene dispersionhas an average diameter of 0.5 μm to 1 μm, 3 to 5 layers, a solidcontent of 5% to 50%, and a residue oxygen content less than 1 wt %, andafter being left to stand for 12 hours, the graphene dispersion has aconcentration distribution increasing from a top section to a bottomsection in a storage container, a viscosity of 5000 cps to 8000 cps, anda graphene concentration of 20 wt %.
 2. The graphene dispersion of claim1, wherein a concentration difference between the top section and thebottom section in the storage container is 0.1 wt % to 20 wt %.
 3. Thegraphene dispersion of claim 1, wherein the graphene powder has 5 to 10layers.
 4. The graphene dispersion of claim 1, wherein an averagediameter of the graphene powder is 3 μm to 15 μm.
 5. The graphenedispersion of claim 1, wherein a residue oxygen content of the graphenepowder is less than 0.1 wt %.
 6. The graphene dispersion of claim 1,wherein the processing solvent comprises a hydrocarbon solvent, ahalogenated hydrocarbon solvent, an alcohol solvent, a phenol solvent, aketone solvent, an ester solvent, an ether solvent, an acetal solvent,an acid solvent, an acid anhydride solvent, a nitrogen-containingcompound solvent, or a sulfur-containing compound solvent.
 7. Thegraphene dispersion of claim 1, wherein the processing solvent has aninterfacial tension of 15 mN/m to 50 mN/m and a Hansen solubilityparameter of 5.0 MPa^(0.5) to 15 MPa^(0.5).
 8. The graphene dispersionof claim 1, wherein based on a total weight of the graphene dispersion,an amount of the graphene powder is 0.001 wt % to 30 wt %.
 9. Thegraphene dispersion of claim 1, wherein the processing solvent has apolar force parameter of 0.5 MPa^(0.5) to 5.5 MPa^(0.5), a dispersingpower parameter of 7.0 MPa^(0.5) to 9.0 MPa^(0.5), and a hydrogen bondforce parameter of 2.0 MPa^(0.5) to 7.0 MPa^(0.5).